Fluorescent manganese activated magnesium gallate phosphor and lamp



J. J. BROWN, JR FLUORESCENT MANGANESE ACTIVATED MAGNESIUM Oct. 22, 1968GALLATE PHOSPHOR AND LAMP Filed Sept 28, 1965 FIGJ WAVELENGTH INANGSTROMS JESSE J. CJzgk FIG.2

ATTORNEY United States Patent 3,407,325 FLUORESCENT MANGANESE ACTIVATEDMAG- NESIUM GALLATE PHOSPHOR AND LAMP Jesse J. Brown, Jr., Towanda, Pa.,assignor to Sylvania Electric Products Inc., a corporation of DelawareContinuation-impart of application Ser. No. 467,898, June 29, 1965. Thisapplication Sept. 28, 1965, Ser. No. 490,931

7 Claims. (Cl. 313-109) ABSTRACT OF THE DISCLOSURE A fluorescentphosphor emitting in the green region when excited by ultraviolet light.The phosphor is magnesium gallate activated by manganese.

This application is a continu-ation-in-part of my copending application,Ser. No. 467,898, filed June 29, 1965, no abandoned.

This invention relates to phosphors which can be excited by ultravioletlight and particularly to a magnesium gallate phosphor activated bymanganese. Such phosphors have been found to emit a narrow band ofvisible light near 5100 A. when excited by 2537 A. ultraviolet radiationwhich makes them particularly applicable to xerographic reproductiontechniques.

Certain gallate-type phosphors have previously been disclosed to theart, however, their emission has not been sufficient or of the properwavelength so that they could be used in xerographic reproductionequipment.

Accordingly, the primary objective of my invention is to prepare aphosphor which when excited by 2537 A. radiation, efiiciently emitslight in a relatively narrow region of the ViSible spectrum at 5120 A.

A feature of my invention is the activation of magnesium gallate bymanganese and its application in fluorescent lamps and high pressureelectric discharge devices.

The many other features, objects and advantages will become manifest tothose conversant with the art upon reading the following specificationwhen taken in conjunction with the accompanying drawings.

Of these drawings:

FIGURE 1 is a perspective view of an aperture-type fluorescent lamputilizing the magnesium gallate phosphor according to my invention.

FIGURE 2 compares the emission spectrum of my magnesium gallate phosphoractivated by manganese with those of the conventionally used zincorthosilicate phos phor and a zinc gallate phosphor activated bymanganese.

Referring now to FIGURE 1, the lamp 1 has a sealed, hollow, glass tube 2containing a filling of 85% argon and 15% helium (although othersuitable gas fillings may be used). On the inside surface of the glassenvelope there is a coating 4 of the magnesium gallate phosphor. Thephosphor coating 4 is shown to extend around about 315 of thecircumference of the tube; the other 45 aperture 5 of the tube left freeof phosphor coating to allow light from the phosphor to emergetherethrough.

The width of the aperture utilized in the lamp is determined by theamount of light which is desired. Thus, sizes other than the 45 abovenoted may be utilized, such as between 20 and 90. The brightness in theaperture area increases as the aperture width is reduced.

At each end of the glass tube 1 there is an electrode comprising anoxide-coated tungsten coil, two auxiliary anodes and associated lead-inwires as shown for example, in a United States Patent No. 2,961,566 ofJohn F. Waymouth et al. for a fluorescent lamp. A usual insulatingplastic base with the base carrying contacts 14 and 15, can be as shown,for example, in United States Patent No.

3,407,325 Patented Oct. 22, 1968 2,896,187, issued July 21, 1959 to R.B. Thomas and E. C. Shappell, for a lamp base, or some suitable base canbe used.

The phosphor coating may be applied at first over the entire glassenvelope by methods well known in the art, and then scraped and brushedoff from the aperture 5 of the glass tube 2, as desired.

Referring now to FIGURE 2, the emission spectral energy distribution ofthe magnesium gallate phosphor activated by manganese is compared withthose of the conventionally used zinc orthosilicate phosphor and a zincgallate phosphor activated by manganese. The spectral distribution curvefor manganese activated magnesium gallate is normalized to with therelative peak intensities of the other two luminophors reducedproportionately.

For the present xerographic reproduction process, it is most desirableto have :a phosphor which has a narrow peak emission in the 5000 to 5300A. region because the characteristics of the copying devices are suchthat the best copies are made in that area.

As is seen from the figure, the magnesium gallate phosphor has arelatively sharper emission of narrower half width than theconventionally used zinc orthosilicate. Moreover the relative peakheight of the magnesium gallate is greater than that of the zincorthosilicate. Each is brighter, of course, than the zinc gallate.

I have discovered that the magnesium gallate phosphor according to myinvention can have the following formula: Mg Ga O :Mn wherein y can bevaried between about 0.001 to 0.05 and the total of x+y can be variedbetween about 0.75 to 1.05. When greater than the upper limits or lessthan the lower limits are used, the phosphor will not fluoresceappreciably and the emission will be shifted somewhat. Comparing lampsprepared using magnesium gallate phosphor to those using zincorthosilicate, I have discovered that my magnesium gallate phosphorproduced 13,188 ft. lamberts at 0 hours, 12,336 ft. lamberts at 96 hoursfor a maintenance of 94% and 10,916 ft. lamberts at 216 hours for amaintenance of 83% whereas a conventional zinc orthosilicate phosphorhad a 100 hour maintenance of only 86% and a 200 hour maintenance of83%.

The luminescent material may be prepared by solid state reaction ofmagnesium carbonate and gallium oxide with the addition of the manganeseactivator in the form of manganese carbonate or any other well-knownmanganese salt. After blending, the mixture is fired between 1000 C. and1400 C. from 5 to 20 hours. Although a weak luminescence is developed atthis point, a second firing in a mildly reactive atmosphere (e.g., 0.01to 1% H in N is necessary to develop an efficient phosphor. This secondheat treatment may vary from 1000 to 1400 C. and be as short as 30minutes. The resulting mixture has the spinel-type crystal structure.

Illustrative of procedures for preparing phosphors according to thisinvention, the following example is cited. This example is cited to showa preferred method of preparing the magnesium gallate phosphor and isnot intended to be limitative upon the claims.

EXAMPLE I The following ingredients are combined in the dry state:

7.256 gm. MgCO 0.115 gm. MnCO 18.744 gm. Ga O This is essentiallyequivalent to 0.854 mole MgO, 1.0 mole Ga O and 0.01 mole MnO. The abovemixture is blended and heat-treated in air in an open Vycor crucible at1400 C. for 17 hours, crushed, and refired at 1200 C. for 1 hour in an N-0.01% H atmosphere. The sample is allowed to cool to room temperaturein the mildly reducing atmosphere with air being carefully excluded. Thereacted product has essentially the matrix composition of MgO.Ga Owherein 0.01 mole of the magnesium has been replaced by manganese.

It is apparent that modifications may be made within the spirit andscope of the instant invention, but it is my intention however to beonly limited to the following claims.

As my invenion I claim:

1. A fluorescent phosphor consisting essentially of magnesium gallateactivated by manganese in suflicient quantitles to produce luminescence.

2. A fluorescent phosphor consisting essentially of magnesium gallateactivated by manganese, wherein the manganese content is between about0.001 to 0.05 gram atom per mole of gallate.

3. A fluorescent phosphor consisting essentially of Mg Ga o zMn whereiny is between about 0.001 and 0.05 and the sum of x and y is betweenabout 0.75 and 1.05.

4. An electrical discharge device comprising: a pair of electrodes; aglass envelope disposed about said electrode; a fill of mercury disposedwithin said device and a coating of a fluorescent material consistingessentially of magnesium gallate activated by manganese in sufficientquantities to produce luminescence, disposed upon the internal surfaceof said envelope.

5. An electrical discharge device comprising: a pair of electrodes; aglass envelope disposed about said electrodes; a fill of mercurydisposed within said device and a coating of a fluorescent materialdisposed upon the internal surface of said envelope, said materialconsisting essentially of magnesium gallate activated by manganese, saidmanganese content being between about 0.001 and 0.05 gram atom per moleof gallate.

6. The device according to claim 5 wherein the total content ofmanganese and magnesium is between about 0.80 and 0.95 gram atom permole of gallate.

7. The device according to claim 6 wherein the phosphor is coated onlypart way around the glass envelope thereby leaving a clear glass slitfor light to emerge therethrough.

References Cited UNITED STATES PATENTS 3,275,872 9/1966 Chernin et al313-109 3,282,856 11/1966 Borchardt 252301.4

OTHER REFERENCES Kroger: Some Aspect of the Luminescence of Solids,1948, pp. 99, 296, 294, and 295..

TOBIAS E. LEVOW, Primary Examiner.

R. D. EDMONDS, Assistant Examiner.

